Different civilizations have developed various technologies which enable communications at superluminal (faster-than-light) speeds over interstellar or even cross-galactic distances.
United Nations Space Command
For much of their spacefaring history, humanity and the UNSC were reliant on starships to carry information across interstellar distances. By the final years of the Human-Covenant War, however, the UNSC had developed technology enabling them to tap into wavespace, a dimensional realm similar to slipspace, to carry messages across short interstellar distances along a series of relays and retransmission stations, allowing colonies and ships to be connected in virtual real real time.[note 1] The energy required to open a wavespace link is immense, however, bandwidth across the relay is limited, and signals carried in wavespace are prone to distortion the further they travel, limiting their effectiveness. Using Forerunner technology, signals can instead be carried across slipspace, allowing colonies and even starships to remain in contact at much faster speeds. The UNSC's discovery of Forerunner technology on Trevelyan in early 2553 enabled even smoother information transfer and the capability for ships to maintain communications while in slipspace; this technology was installed on the UNSC Infinity and select ONI vessels.[note 2] Such communicators can be built compact enough to fit into man-portable communications kits. UNSC Infinity's superluminal communications capability includes 16-channel "slipspace wavecom datalinks".
This system may be related to a form of communication known as "slipstream packets", which are, in essence, recorded audio messages, rather like letters. Human civilians were able to use slipstream packets by September 2552. These messages are sent through Waypoint, a UNSC communications network similar to the 21st-century Internet.
Before the advent of superluminal communications, most human long-range communiques were carried on the shipboard memory of starships such as automated freighters. On the other end of the ship's slipspace journey, the message would be relayed to the intended recipient. At the time of the establishment of the Cole Protocol in 2531, while unable to send messages through slipspace itself, the UNSC was able to use a form of slipspace manipulation to obfuscate radio transmissions sent from Earth centuries earlier in order to prevent the Covenant from using the signals to triangulate Earth's location.
The UNSC also developed a piece of technology known as the Slipspace COM launcher, which sent independently guided probes through slipspace as fast as any UNSC starship. The strength of this system was the probes' ability to precisely home in on the designated target and securely deliver the message to the recipient. However, this technology was highly expensive and as a result there were only three such launchers in existence by 2552: one on Reach, one on Onyx and one on Earth. As of the conclusion of the Human-Covenant War, both the devices on Reach and Onyx have been destroyed, with the fate of the Earth device unknown.
The Forerunners had virtually abandoned the electromagnetic spectrum as a means to carry their communications, instead relying on more secure quantum entanglement. These communications were routed over proprietary encryption protocols, which could be used to track the source or destination of the communication. This allowed instant data transfer over vast distances: Offensive Bias, for example, was capable of simultaneously coordinating the deployment of the Halo Array at Installation 00 outside the galaxy and its fleet of war at the Maginot Line.
The Domain, the Forerunners' collective information repository, was not usually employed for the purpose of communications due to its unreliability: it had a known propensity to alter information without explanation. However, it was still known to be used for communications on certain occasions.
The Forerunners also used a form of superluminal communication involving wormholes; however, these communications were significantly slower than communication via the Domain.
During the Battle of Installation 05, Cortana was able to utilize Forerunner technology to send an emergency signal directly through slipspace, without a physical carrier, declaring codes Bandersnatch and Hydra. According to Endless Summer, the energy required to send such a transmission would have required more energy than the combined output of all UNSC assets, demonstrating the Forerunners' superior grasp of energy manipulation. However, this appears to have been an ad hoc or emergency communication system given the Forerunners abandonment of wave-based communication, likely carried within the anomalous wake of the Forerunner Dreadnought's passage to the Sol system.[note 3]
Forerunner starship sensors were capable of instantaneous scanning and detection across interstellar distances. As a particularly impressive example of their available sensor ranges, the Forerunners' core authority routinely tracked individual slipspace jumps across the galaxy. Forerunners shipboard sensors were also capable of providing a detailed analysis of a single planet's geological and ecological composition from light-years away through the use of long-range entanglements.
The Covenant use slipspace as the basis of their virtually instantaneous interstellar communications, having developed such technologies from the analysis of Forerunner technology. When installed on a planet, for example, Covenant communications relays enable communications to corresponding devices across many light-years. Known as the proselytization network, Procurator supply ships were fitted with such systems in order to keep fleets connected to High Charity and to help spread the power and influence of the Prophets across Covenant space. At the Covenant hegemony's height, their starships possessed an automated messaging system which transmitted new orders and communiques from ship to ship upon arrival at or departure from a given star system, enabling them to rapidly relay information across their vast empire. However, as noted by Cortana, these messages were not properly encrypted by UNSC standards, perhaps due to the Covenant's arrogance or ignorance of the workings of their own technology.
The Flood's collective intelligence, the Gravemind, employs an esoteric mechanism which can quite aptly be described as telepathy, controlling Flood forms across vast distances. In certain circumstances, the Gravemind has also demonstrated to be capable of using this ability to telepathically communicate with non-Flood beings, namely John-117.
- In Halo: The Fall of Reach Chapter 16, Captain Jacob Keyes contacts Vice Admiral Michael Stanforth from the Sigma Octanus system on a FLEETCOM priority channel and they have a real-time exchange. Stanforth is implied to be in a different system at the time. In addition, in her journal, Halsey receives an after-action report of the Battle of Sigma Octanus IV on July 18, 2552, the same day the battle took place. This would be impossible without a near-instantaneous communications system, as a ship could not have possibly traveled from Sigma Octanus system to Reach in a matter of hours; it took two weeks for Battle Group Leviathan to make the journey. Furthermore, according to page 122 of the Halo Graphic Novel, some sort of superluminal communications system was used by Dr. Catherine Halsey to contact Earth while onboard the UNSC Gettysburg. The transcript seems to show Halsey transmitting commands in real time. Even if this is accomplished using a script, it still takes about 36 minutes for the data to be transmitted from Earth to somewhere near Eridanus Secundus. The log in the Graphic Novel has an opening timestamp of 04:16 on September 12th, 2552; chapter 27 of Halo: First Strike opens at 04:50 on September 12th, at which point the data has apparently been received. The distance is unknown, however, and so the exact speed can not be calculated. Further examples of such superluminal communication are seen in the Data Drops.
- In Halo: Mortal Dictata, it is stated that the discoveries on Trevelyan are what enabled the UNSC instantaneous interstellar communications. Since there are multiple examples of effectively real-time communication before the discovery of the shield world in earlier media (including the first Kilo-Five Trilogy novel Halo: Glasslands) it can be assumed that the discussed upgrades improve the system already allowing practical near real-time correspondence on timescales imperceptible to humans but relevant to AIs and data transfer.
- In Halo: Ghosts of Onyx, the prowler UNSC Dusk is implied to have followed the Forerunner Dreadnought's slipspace wake, making it to Earth within hours. This creates an inconsistency with later canon, such as this timeline, which reveals that the Dreadnought took five days to reach the Sol system and another nine days to reach Earth, instead of a few hours. Therefore, the Dusk's speedy return to Earth may have been the result of a Slipspace anomaly, something that is indeed mentioned by the crew of the Incorruptible as taking place in the slipspace dimension YED-4, and likely acted as the carrier of Cortana's message.
- Halo: Warfleet p.10
- Halo: The Thursday War, page 287
- Halo: Mortal Dictata, page 202
- Halo: Glasslands, page 418
- Halo Mythos, pages 132-133
- i love bees: week6_subject3.wav
- Axon Clips: Chapter 6
- YouTube: Halo: From A to Z with Frank O'Connor
- Halo 4 Limited Edition, Infinity Briefing Packet (Ship R&R Opportunity Schedule)
- Halo: Contact Harvest, page 35
- Halo: Evolutions - Essential Tales of the Halo Universe, "The Impossible Life and the Possible Death of Preston J. Cole", page 469
- Halo: Ghosts of Onyx, page 176
- Halo: First Strike (2010), "Tug o' War"
- Halo: Blood Line, Issue 1
- Halo: Cryptum, page 144
- Halo: Cryptum, page 125
- Halo: Silentium, pages 326-328
- Halo: Combat Evolved Anniversary, Terminal 4
- Halo: Ghosts of Onyx, page 182-183
- Halo: Cryptum, page 136
- Halo: Silentium, page 121
- Halo Waypoint: Covenant
- Halo: Mortal Dictata, page 215
- Halo: Warfleet, p. 68
- Halo: First Strike, pages 197-198
- Halo 3, campaign levels Floodgate, Cortana